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Nov. 12, 1946.
, s, A, SCHERBATSKOY
SEISMOMETER
Filed June 10, 1943
RECORDER
2/6
2/2
2/4
2/.?
2/0
220
22/
t
‘
I
2,411,117
Patented Nov. 12, ‘19146 1
UNITED
2,411,117
. SEISMOMETER.
Serge A. Scherbatskoy, Tulsa‘, Okla., assignor to
Seismic Engineering Company, Dallas, Tex.
Application June 10, 1943, Serial No. 490,373
1 Claim. (01. 177-352)
.
This invention relates to a detector of seismic
waves or what is commonly known as a seis
mometer.
.
With similar objects in View, a number of de
vices of this nature have been used in the past.
~
These may be roughly classi?ed as:
i
(a) Mechanical devices such as are usually used
' for recording natural earthquake waves;
2
.
by means of explosives or otherwise and the re
sulting seismic waves after refraction and/or re—
?ection from sub-surface formations are detected
by seismometers.
'
It is a further purpose of my invention to pro
vide an improved form of construction of vibra
tional resistances of the type referred to. This
construction relates particularly to vibrational
electrolytic resistances in which the distance be
(b) Electrostatic devices in which the space be
tween two condenser plates is varied by the earth 10 tween the electrodes can be varied when the device
movements;
is exposed to the vibrations that it is desired to
(0) Piezo-electric devices in which crystals
having piezo-electric properties are stressed by the
earth movements, thus generating electric cur
rents;
(d) Bolometer devices in which bellows actuated
by seismic waves force air currents to pass through v
bolometers, thereby varying the bolometer poten
tials;
'
measure or to detect.
,
In general, it is an object of my invention to
provide a device for translating mechanical vi
brations into electrical currents which involves
the principle of varying the distance between elec
trodes immersed in an electrolyte. Such a device
may be constructed in an ef?cient and compact
manner similar to well known other devices for
(a) Electromagnetic devices of the moving coil 20 translating mechanical vibrations into electrical
variety, in which the position of a coil or coils
currents. Other objects and advantages of the
relative to a magnetic ?eld of substantially con
stant strength is varied by the earth movements“
invention will be apparent from the following de
scriptions when read in conjunction with the
causing a cutting of magnetic lines of force by the
drawing, in which:
'
coil or coils thus‘ generating electric currents or 25 Fig. 1 shows ‘constructional details of my device
potentials therein; and
'
in a vertical cross section and includes also‘an
' (f) Electromagnetic devices in which the re
luctance of a magnetic circuit is varied by earth
movements, and the resultant’ variable ?uxes are
interlinked with electric coils in which corre
sponding" electric currents or potentials are gen
erated.
,
electrical network connected to the device, the
_ ‘said network containing a Wheatstone bridge.
One arm of the bridge consists of the electrolytic
The network is’ ener
gized with A. C. current.
30 resistance of my device.
Fig. 2 shows a horizontal cross section of the
The above devices can, of course, be used to de
device illustrated in Fig. 1, the said cross section
tect and/or record disturbances, vibrations or
being taken along a line ab in Fig. 1.
movements in any type of material with which 35 Fig. 3 shows the device illustrated in Fig. 1 and
they are in contact and are not con?ned to the
includes also an electrical network connected to
study of natural or arti?cial earthquakes.
the device and energized by a D. C. current.
It is the purpose of my invention to provide a
Fig. 4 shows schematically my device in a modi
new type of seismometer utilizing an electrolyte
?ed form and includes also an electrica1 network
and two electrodes immersed in the electrolyte 40 connected to the device, the said network being ‘
and in which the distance between the electrodes
energized by an A. C. current and containing a is varied by the earth movements. Such a seis
Wheatstone bridge two arms of which consist of
mometer will be included in a suitable electrical
the electrolytic resistance of my modi?ed device.
network energized by a source of electrical energy
Before proceeding with a detailed description it
and across the output terminals of the electrical 45 should be mentioned that any seismograph,
network, electrical currents will be obtained which
whether electrical, mechanical, or otherwise, con
will correspond to the seismic waves impinging on
sists essentially of a frame and of a vibrating mass ,
the seismometer. These electric currents, with
attached to the frame. The connection between
or withut suitable ampli?cation, are transmitted
the frame and the vibrating mass is in nearly all
tooscillograph elements, the movements of which 50 cases elastic, that is, it consists of a spring which
are recorded 'on a moving photographic strip and
permits the vibration of the mass. The period
represent graphically vibrations caused by the im; ‘ of vibration of the mass is adjustedby means of
pinging seismic waves. Such a seismometer is
the constants of the spring or by means of addi
particularly adapted to the art of seismicsurvey
tional auxiliary springs. Whenever the‘ ground '
ing in which arti?cial earthquakes are generated 55 upon which the seismograph
is standing vibrates,
2,411,117
4
3
as from a natural or arti?cial earthquake, the
servation and consequently under the aforemen-I
frame of the instrument moves with the ground;
tioned conditions when the casing is stationary
the electrolyte resistance between the electrodes
22 and 23 has a ?xed and predetermined value,
because the distance between the electrodes 22
and 23 is ?xed and predetermined.
the mass, which is usually referred to as the
"suspended mass,” remains substantially at rest.
The relative motion or displacement between
frame and suspended mass is then utilized for the
generation of an electric current in the case of ,
an electric seismograph or in the case of a me
chanical seismograph directly actuates a. record
ing-stylus after suitable magni?cation by means
of levers.
'
Referring to the drawing and more particu
larly to Figs. 1 and 2 of the drawing, I have pro- -
It is-readily appreciated that if the casing I8
is moved 'up and down, for instance by sound
vibrations or otherwise, the inertia‘member I‘!
will tend to remain stationary and the distance
between the electrodes 22 and‘23 will vary.be-,
, cause of the ?exibility of the walls of the con
tainer 2| which will produce bellows-like mo
tions by allowing the volume of the container to
vided a casing Ill adapted to be buried or other
wise anchored to the ground so that it will be 15 alternately expand and contract. It is obvious
that the variation in the distance between the -'
responsive to slight movements or vibrations of
l electrodes 22 and 23 will cause variations in the
- the ground, such for instance as those which
The
electrolytic resistance between these
Consequently, changes in electrolytic
casing is provided with a cover member || se-' 20 between the connecting leads 28 and
produced by a passing seismic wave
cureiy attached to the casing In by suitable screws
electrodes.
resistance
29 will be
when the
A ledge I3 is formed on the inner surface
casing I0 is buried or otherwise anchored in the
might be produced by the passage through the
ground of sound or compressional waves.
I2.
of the casing and to this ledge is rigidly secured
ground.
The electrolytic resistance of the geopho'ne is
membrane l5, made preferably of thin ?exible 25 measured by means of a Wheatstone bridge 40.
The bridge is shown as formed by four resistances,
steel. The elastic membrane I5 is in the form
such as resistors 4|, 42, 43 and the varying elec
of av ring having its outer periphery rigidly seé
trolytic resistance inserted between the leads 28
cured to the ledge I3 and having its inner periph
by means of suitable screws l4 an annular elastic
ery rigidly connected to an inertia member which
consists of a steel cylinder |'| having a relatively
large mass. Within the lower part of the casing
Hi there is arranged an electrolytic cell 20 which
consists of a. container 2| ?lled with a suitable
and 29. A source of alternating current 44 of a
vfrequency f is applied between the terminals 45
and 46, the terminal 45 being the point of junc
tion of the resistor 43 and the lead 29 and the
terminal 46 being they point of junction of the
resistors 4| and 42. The resistors 4|, 42 and 43
electrolyte and of two electrodes 22 and‘ 23 im
mersed in'the electrolyte at suitable distances 35 have been so chosen that when the casing I0 is
stationary the ratio of resistance 4| to resistance
one from the other. The container 2| is of a
42 is equal to the ratio of the electrolytic‘re
cylindrical bellows-like form. It has its base se- .
sistance to the resistance 43. It can readily be
_ curely attached to the bottom oi the casing -| 0 and
. shown that the bridge is “balanced,” that is, the
is provided with a cover 24 having the form of
a a steel disc and rigidly connected to the inertia 40 potential di?erence resulting from the source 44
and applied across the terminals 45 and 46 will
member H by means of a rod 25. The walls of
cause no potential difference- to, exist between
the container 2| are made of thin undulated
terminals 50 and 5|, the terminal 5|] being the
elastic sheet which gives to the container a bel
point of junction of the resistor 4| and of the
lows-like appearance. The walls are ?exible and
therefore make it possible for the container to 45 lead 28, and the terminal 5| being the point of
junction of theresistors 42 and 43. The terminals
expand or to contract by increasing or decreasing
50 and 5| are connected to the primary windings
_the distance between the top cover 24 and the
of the transformer 54-, the secondary windings
bottom of the casing. The electrodes 22 and 23
are rigidly connected to the cover 24 and the ’ of which are connected to the input terminals of
bottom of the casing respectively, and therefore, 50 an ampli?er 51. Thus under such circumstances
no matter what voltage is derived from the source
when the container 2| is subjected to bellows
44 no signal appears across the output terminals
like motion by expanding or contracting its
of the ampli?er 51.
'
volume the distance between the electrodes 22
As described in the preceding paragraphs-the
and 23 alternately increases or decreases.
Electrical connecting leads 28 and 29 are se 55 geophone consists of a casing III which is the
wave responsive element adapted to be buried or
cured to the electrodes 22 and 23 respectively.
anchored in the ground or other medium in order
These connecting leads pass outwardly from the
to partake in'the vibration. The inertia element
casing through a stu?ing box 30 provided with
H is mounted upon the diaphragm I5 in such a
a suitable packing 3|.
'
' If the casing I0 is stationary an equilibrium 60 relation to the casing III that a relative move
ment will be produced between the inertia ele
condition is reached between the pull of gravity
ment and the‘ casing whenever a. vibration or
upon the inertia member H and the correspond~
train of waves strikesthe device. An electrolyte
‘ing reaction of ‘the resilient membrane Hi. This
is provided within the device and suitable elec
condition is characterized by a certain geometri
. cal con?guration of» the whole assembly in which 6.5 trodes are arranged within the electrolyte in such
a manner that the relative distance between the
= the electrodes 22 and 23 are spaced one from the
electrodes 22 and 23 varies in accordance with
other at a certain predetermined distance. It is
the relative movement between the casing l0 and
well known that the electrolytic resistance be
the inertia element l'l. Consequently, whenever ,
tween the electrodes 22 and 23 depends upon the
resistivity of the electrolyte which is a function 70 a vibration or a train of waves strikes the geo- '
phone the resistance of the electrolyte as viewed
of factors such as the nature of the electrolyte,
from the leads 28 and 29 is varied in accordance
its concentration, temperature, etc., and also de
with the said vibration or said train of waves.
pends upon the distance between the electrodes.
Now assume that the geophone is properly in
The resistivity of the electrolyte is assumed to
be known and constant during the process of ob-; 75 serted in the ground and a vibration is received
‘2,411,117
-
_
'
5
I
which tends to move the casing upwardly. Due
to the inertia of the member I1 the distance be
tween the electrodes 22 and 23 decreases and con
sequently the electrolytic resistance as viewed
from the leads 28 and 29 decreases. It will be
readily appreciated that under such conditions
the ratios between the resistance 63 and the elec
6
-
-
.
signal supplied from terminals 41a, 41b and the
signal. supplied from terminals 15a, 15b. '
Consider now the ring modulator circuit con
tained in the rectangle 60. The circuit shown
therein comprises a bridge circuit consisting of
four recti?ers BI, 82, 83.84 each of the said rec
ti?ers constituting a separate arm of the bridge
trolytic resistance changes and the bridge be- 7
comes unbalanced and as the motion of the cas
circuit and arranged so that the current can flow
only in an anticlockwise direction. The upper
ing upwards-continues, the said ratio ‘departs
10 corner of the bridge 85 and/the lower corner of
more and more from the balanced cdndition.
Consequently, an unbalance voltage appears
across theoutput terminals 'of the transformer
54, the. magnitude of this voltage increasing with
the motion of the casing [ll in the upward direc 15
tion. After having attained a certain maximum
displacement in the upward direction the geo
phone casing begins to move downward, passes
through the original neutral position and con
tinues its downward motion.
Then the corre
sponding unbalance voltage across the output
the bridge 86 are respectively connected to the
input terminals 41a, 41b and are also connected
one to another by means ‘of equal resistances 81
and 88 in series. The other corners of the bridge
89, 90 are respectively connected. to the output
terminals 16a, 16b and'are also connected one to
another by a pair of equal resistances 9i, 92 in
I series, The other input terminals 15a, 15b of’ the
ring modulator are respectively connected to the
20 point 93 connecting the resistances 81, 88 and to
the point 94 connecting the resistances 9|, 92.
terminals of the transformer 55 decreases its
magnitude, passes throughthe zero value, sub- _
sequently it reverses its polarity and increases
again with the downward motion of the casing
Hi. It is therefore apparent that the unbalance
. voltage appearing across the output terminals
of the transformer 55 is being represented by a
modulated carrier, the frequency of the carrier
being the, same as that of the source lid and the
modulation varying in accordance with the mo
tion of the geophone casing It. It is desired to
reproduce electrically the geophone motion and
I am accomplishing thispurpose by demodulat
ing the unbalance voltage derived from the
Wheatstone bridge.v Consequently in such an ar_
With the circuit as described, current derived
from the terminals dl'a, d‘lb may ?ow either
' through the recti?ers 82, 83 or through the recti
?ers 8d, 8! depending upon its direction, but it
can never flow through all the four recti?ers at
the same time, since the recti?ers 82, 83 on one
hand and the recti?ers 8%, 8| on the other hand
- are arranged to flow in opposite directions.
Suppose now for purpose of illustration that
the voltage derived from the terminals l5a, 75b
and the unbalance voltage derived from the ter-.
' minals é‘ia, d'lb are simultaneously applied, and
vsuppose that both voltages are in phase, i. e., the
. jterminal e‘la becomes positive as compared to the
terminal ?ll; and at the same time the terminal
rangement the instantaneous value or‘ such a de- ‘
75a becomes positive as compared to the terminal
75b. Then one part of the current tends to flow
modulated voltage will represent at any instant
the magnitude of the displacement ofthe casing I from the terminal 150. to the terminal 93 and
ill from its neutral position and the polarity of 40 through the resistor ill to the terminal 85 and
then through the recti?er 82 and through the re_
this voltage will indicate at any instant whether
or not the impressed displacement has been
sistor 5i back to the terminal 752). The other
part of the current tends to flow from the termi
c?‘ected in the upward or in the downward direc
tion. In order to accomplish this purpose I am
nal 15a to the terminal 93 and through the re- ‘
amplifying the output voltage derived from the
sistor 88 back- to the terminal 86 and through the
recti?er 85 and through the resistor 92 back to
unbalanced bridge in an A. C‘. ampli?er r'il' and
am subsequently applying the output terminals
the terminalitb. The currents ?owing through
of the ampli?ers! to a, ring modulator contained
the resistors iii, 92 are equal and of opposite
within the dotted rectangle B6. The ring modu
lator 6!! is provided with two pairs of input ter
minals 41a, Nb and 15a, ‘25b respectively and one
directions.
>
It is apparent that under the conditions de
scribed in the preceding paragraph the polarity
of the terminals 85, 86 will be positive with re-_
pair of output terminals 76a, 75b. The input ter
spect to the polarity of the terminals 961, 89. Con
minals 61a, Alb are connected to the output of
sequently, positive voltages are applied to recti
the ampli?er 57, the input terminals ‘55a, ‘55b
receive the output from the source of voltage M 55 ?ers 82. 8t. Therefore, these recti?ers will lose
their ability of rectifying currents, and Will allow
' and the output terminals 76a, 76b are connected
currents to traverse them in both directions. At
to a recorder included in the dotted rectangle 99.
the same time negative voltages are applied to
The ring modulator is well known in the art'
recti?ers iii. 88; consequently, the recti?ers 8|,
and has been described in an article by R. S. Car
ruthers on “Copper oxide modulators in carrier 60 '83 will retain their rectifying ability and vwill
block currents attempting to traverse them in the
telephone systems,” the Bell System Technical
negative direction. Therefore, the recti?ers B2
Journal, vol. XVIII, 1939, pp. 315-337. The type
and 8d are conductive in both directions, and
of the circuit contained in the dotted rectangle
consequently, when the unbalance voltage is be
6B is illustrated in Fig. 2c page 318 of the said 6
ing developed across the terminals élla, Mb, we
article. The ring modulator is essentially a dou
?nd that a current tends to pass from the termi
ble balanced modulator. By double balanced is
nal GM to the terminal 8-5 and then through the
meant a modulator in which each input is bal
recti?er 82 through the resistors 9| and 92 to
anced out from the output, and the output con
the terminal 90 then through the recti?er 813 back
tains therefore substantially only the modulation 70 to the terminal d‘lb. This current superposes it-v
products.
self upon the current which is already flowing
Across the output terminals 16a, 16b of the
through the resistors 9| and 92 and consequently
modulator 60 therefore appears a signal which
the resultant current passing through the resistor
among other modulation products contains sig
ill becomes larger than the current passing
nals‘ corresponding to the product between the 75 through the resistor 92, consequently, the balanc
2,411,117
ing that existed before is offset because there
I02,v I03 and I04. The resistor I04 is in series
is a situation where the current flow through the
with the electrolyte of the geophone, the resistor
resistor 9| is increased as compared to the cur
I02 is in series with the resistor I03, and the re
rent ?ow through the resistor 92. Thus the volt
sistors I02, I03 are in parallel with the resistor
age drop across the resistor 9| becomes greater
I04 and the electrolyte. The battery MI is con
and a positive overall voltage is developed across
nected across the diagonal points ‘I05 and I06 of
the bridge. The other diagonal points I01, I08 '
the terminals 16a, 1612. It can be-also readily
seen that when the unbalance voltage applied
are connected to the input terminals of an am
across the terminals 41a, 41b increases in mag
pli?er I I0 the ‘output terminals of which are con
nitude the corresponding resultant voltage ob 10 nected to the recorder III. The recorder III is
tained. across the output terminals 76a, 16b in
of a construction similar to the recorder 99 in
creases in magnitude also.
Fig. 1.
It can be shown that if the polarity of the
When the casing‘of the geophone is stationary,
?rst input voltage would reverse with respect to
i. e., in the absence of any seismic excitation, the
the second input voltage, i. e., if we suppose that 15 resistance of the electrolyte between the leads 28,
the terminal 15a becomes positive as compared
29 depends upon the surrounding temperature.
to the terminal 15b and the terminal 41a becomes
In order to compensate any possible variations in
negative as compared to the terminal 41b then
the ambient temperature the resistor I04 of the
the balance becomes offset in the opposite direc
bridge is made adjustable and its value is so ad
tion, because there is a situation‘where the cur 20 justed that it is exactly the same as the-resist
’rent flow through the resistor 92 is increased as
ance of the electrolytein the geophone. The re
compared to the current ?ow through the re
sistances of the arms I02 and I03 are made equal
sistor 9|. Then the voltage drop across the re
one to another. Under such conditions the bridge
sistor 9| becomes smaller and the overall volt
is balanced and no voltage appears across the
age developed across the output terminals 16 has 25 input terminals of the ampli?er IIO. Conse
I a polarity opposite to the case described above.
‘ It can also be shown that in an intermediate
quently, the signal applied to the recorder III
is zero.
‘
situation where the signal voltage derived from
the input terminals 15a, 15b is displaced by 90
When, however, the geophone casing I0 is
bridge and applied across the terminals Ma, 47b
f, modulated by the geophone motion according
balance of the bridge. Consequently, when the
motion of the casing I0 upwards continues, the
unbalance of the bridge continues and the volt
to a function A(t) which represents the varia
age across the output terminals of the amplifier
moved upward by an incoming seismic wave, the
degrees with respect to the voltage derived from 30 resistance of the electrolyte between the leads
the input terminals 41a, 41b then the D. C. volt
28, 29 decreases. Consequently the bridge I00
age output from ring modulator is zero.
'
becomes unbalanced and a D. C. voltage appears
Let us designate the voltage applied across the
across the output terminals of the ampli?er “0.
terminals 15a, 151; as E1 sin 21:- ft. Then the
It can be readily appreciated that the magnitude
unbalance voltage ‘derived from the Wheatstone 35 of the said voltage represents the degree of un
can be represented by a carrier of the frequency
tion of the instantaneous displacement of the 40 H0 becomes larger. When, however, the motion
geophone casing Withrespect to time.
of the casing upwards has attained a maximum
Consequently, the unbalance voltage can be
and then decreases by passing through the nor
represented by the following expression: Ad) sin
mal equilibrium position the voltage across the
21r it. It can be readily appreciated that under
terminals of the ampli?er H0 decreases and
these conditions the voltage derived from the 45 reaches the value zero.
output terminals 16a, 16b of thering modulator
The seismic disturbances striking the geophone
varies with time as the function Mt), i. e., this
are of an oscillatory character and therefore they
voltage represents theearth motion. The volt
cause the casing of the 'geophone to move up
age derived from the ring modulator is subse
wards to a maximum upward displacement then
quently applied to the recorder 99.
50 downwards through the neutral position to a
The recorder 99 may be of conventional type
maximum downward displacement then back to
used in seismic prospecting, which includes a
the neutral position, etc. It is readily apparent
moving coil galvanometer connected to the ter
that when the casing passes through its neutral
minals 16a, 16b having a mirror“ attached to
position in the downward direction, the unbalance
its coil. This galvanometer isjarranged in such 55 voltage across the output terminals of the am
relation to a moving strip of sensitized paper 62
pli?er I I0 reappears again with a polarity which
and to a light source 63 so as to record on the
is opposite to the one referred to in the preced
paper a wave form or “trace” which has its lon
ing paragraph. Consequently, the polarity of
gitudinal axis parallel with the longitudinal axis
the unbalance voltage appearing across the out
of the strip of paper.‘ This strip of paper is 60 put terminals ofthe ampli?er I I0 represents the '
moved longitudinally at a substantially constant ‘ upwards or downward direction of the impressed
speed by means of a‘ motor 64.
displacement, and the magnitude of the voltage '
Fig. 3 illustrates another embodiment of my
represents the magnitude of the displacement.
invention in which in place of_ an A. C. source of
The unbalance voltage derived from the ampli
electrical energy a D. C. source is used. The geo 65 ?er H0 is recorded in the recorder III and pro
phones used in the arrangements of Fig. 1 and
vides a representation of the corresponding seis
of Fig. 3 are of an identical construction. In
mic disturbances.
‘
.
Fig. 3 however, the output leads 28 and 29 of
We shall consider now the most suitable elec
the geophone are connected to a Wheatstone
trolytesmthat may be used in order to provide a
bridge circuit I00 which is energized by a D. C. 70 variable A. C. resistance in the embodiment of
source of voltage, which is ‘represented by a bat
Fig. 1' or a variable D. C. resistance in the em
tery I0l. One arm of the Wheatstone bridge
consists of the ‘electrolytic resistance inserted be
tween the leads 28, 29v, and the remaining three
- bodiment of Fig. 3.
vElecI:._1_'olytic- resistors of many‘ types and kinds
have been madelingthe past, but most or them
arms of the bridge circuit consists of resistors 75 were‘ subject tolimitstions oi’ polarization, gass
2,411,117
16
ing, non-uniformity or lack of permanence. The
use of electrolytic resistors has been con?ned
therefore to applications in which these detri
mental features were not objectionable or for
which they possessed _some positive advantages.
Because of polarization and gassing when used
with direct currents, electrolytic resistors are
more generally associated with A. C. circuits.
However, certain types may be used successfully
in D. C. circuits.
_
moved upwards or downwards by incoming seis
mic vibrations, then the intertia member 2!‘! will
tend to remain stationary and the distances be
tween the electrodes 222 and 220 from .the inter
mediate electrode 22! will correspondinglyvary. ~
‘It is obvious that the variation in the distance
between these electrodes will cause ‘variations in
the electric resistance between the electrodes. '
Consequently, a passing seismic wave will cause
10 a motion of the geophone which will in turn pro
'I'he electrolyte used in the devices shown in
duce variations in the electrolytic resistance be
Fig, l or Fig. 3 may consist of copper sulphate
tween leads 230, 23! and the leads 23! and 232
respectively. Thesevelectrolytic resistances are
and the electrodes of copper plates or of mercury
inserted into a Wheatstone bridge 250. The
nitrate with mercury electrodes, or any other
combination of electrolyte and electrodes such 15 bridge is formed of a series of four resistances
that the passage of current through the electro
such as the resistors 24!, 222, the varying elec
lyte does not cause any change in the chemical
trolytic resistances inserted between the leads
constitution of the electrolyte or of the electrodes
230, 23!, and the varying electrolytic resistances
and no gases are generated. Such an electrolyte
inserted between the leads 23!, 232. A source of‘
may be used in connection with A. C. or D. C. 20 alternating current 244 of a frequency f is ap
currents.
plied across the terminals 245 and 226, the ter
Instead of employing electrodes and an electro
' minal 2&5 being connected to the lead 23H and
lyte which undergo no change in their chemical
the terminal 2E6 being‘ a point of junction of the
constitution 'by the passage of the current, elec
resistors 24! and 242, The resistors 24! and 2132
trodes and an electrolyte in which such change 25 have been shown to be equal one to the other so
does occur may be employed, but in this case it is
that when the casing 2 I0 is stationary the bridge
desirable to select the electrolyte and the elec
is balanced, i. e., the potential difference result
trodes so that the chemical changes are revers
ing from the source 244 and applied across the -'
ible, whereby permanent change in the chemical
terminal 255, 2% will cause no potential di?‘er
constitution can be prevented by reversing the 30 ence between the terminals 250, 25!, the terminal
direction of current ?ow from time to time. Such
250 being the point of junction of the lead 230
an arrangement is illustrated in Fig. 1 an A, C.
and the resistor 24! and the terminal 25! being
. source is being supplied to the terminals t5 and
the point of junction of the lead 232 and there
436 of the Wheatstone bridge and causes periodic >
sistor 262. The terminals 250, 25! are connected
reversals of the current passing through the elec 35 to the primary windings of the transformer 252
trolyte between the electrodes 22 and 23.
the secondary windings of which are connected
Consider now Figure 4 representing. an im
to the input terminal of the ampli?er 251. As
proved system for deriving a voltage from a vary
sume that the geophone is properly inserted in
ing electrolytic resistance. The geophone shown
the ground and vibration is received which tends
in the ?gure and designated by the numeral 206 40 to move the casing 240 upwards. Due to the
consists of a casing 2!!) adapted to be buried in
inertia of the member 2!‘? the distance between
the ground so that it will be responsive to the
the electrodes 222 and 22! decreases and the dis
vibration of the ground. The casing is provided
tance between the electrodes 22! and 22!! in
with a cover member 2!! securely attached to the
creases. Consequently, the ratio of the electro
casing 2 ill by suitable screws 2J2. A ledge 2 i3 is 45 lytic resistances between the electrodes 222, 22!
formed on the inner surface of the casing and to
and 22E , 22!) increases and the bridge 250 becomes
this ledge is secured by means of suitable screws
unbalanced. It is apparent that the more the
2 It an annular membrane 2 ! 5 made preferably of
casing 2 it becomes displaced in the upward direc
thin ?exible steel. The membrane 2!5 is in the
tion the more unbalanced becomes the bridge and
form of a ring having its outer periphery rigidly 50 the larger is the unbalanced voltage derived
secured to the ledge 2 i3 and having its inner pe
from terminals 250 and 25!. This unbalanced
riphery rigidly connected to an inertia member
voltage is being represented by a modulated car
which consists of a steel cylinder 2!‘! having a
rier the frequency of the carrier being the same
relatively large mass. Casing 220 contains an
as that of the source 246 and the modulation
electrolyte which ?lls it almost completely, the 55 varying in accordance with the motion of the
upper level of the said electrolyte being desig
geophone casing 21%. It is desired to produce an
nated by 2 !8. Within the electrolyte 3 electrodes
electrical current that is a facsimile of the geo
are immersed: an upper electrode 22d, interme
phone motion and I accomplish this purpose by
diate electrode 22! ‘ and a lower electrode 222.
demodulating the unbalance voltage derived from
The electrodes 226 and 222 are rigidly secured to 60 the Wheatstone bridge by means of a ring modu- "
the casing 2H3 by means of bars 225, 225 respec
lator 260 having its input terminals 261a and
tively and the electrode 22! is, rigidly secured to
2511) connected to the output of the ampli?er
the inertia member 2!? and participates in the
motions thereof. Electrical connecting leads 23G,
25‘! and. having its input terminals 215a, 2151)
from the intermediate electrode 22i by predeter
designated by the numeral 29 in Fig. 1. Thus I
23! and 232 are respectively connected to the 65 connected to the source of voltage 254. The ring
modulator 250 is of a construction substantially
electrodes 22B, 22! and 222.
'
.
similar to the one described by the numeral 60 in
vVil'hen the casing 2H} is stationary an equilib
Fig. 1. Consequently, the voltage derived from
rium condition is reached between the pull-of
the output terminals of the ring modulator 26d
gravity upon the inertia member 2 I l and the cor
responding reaction of the resilient membrane 70 varies with time as the displacement of the geo
phone casing. This voltage is subsequently ap
2i5. This condition is characterized by a certain
geometrical con?guration of the whole assembly
plied to a recorder 299 which is of the conven
in which the electrodes 22d and 222 are spaced
tional type substantially similar to the recorder
‘ mined amounts.
If, however, the casing H3 is 75 obtain by means of the recorder 299 a wave form
2,411,117
11
i
'12
or trace representing the vibration to which the
casing'rand below said membrane. a conductive
geophone is subjected.
liquid within said container, electrodes immersed
in- said liquid and suitably positioned within said
I claim:
A geophone for translating the earth vibrations
into corresponding electrical oscillations, said
geophone comprising an outer casing adapted to
container in a de?nite spacial relationship one to
another, connecting elements between said elec
trodes and said outer casing and said inertia
member, respectively, whereby variation in the
be subjected to the earth vibrations, an inertia
spacing between said electrodes is produced in
. member within said casing, a ring-like elastic
response to said vibration and the resistance of
membrane having its outer periphery secured to
the inner walls of said casing and having its 10 said liquid between-said electrodes varies in ac
cordance with the variation in said spacing,
inner periphery secured to said inertia member, a
.
sman A. SCTSKOY.
?exible bellows-like container located within said‘